We were big fans of the Raspberry Pi 400 when it launched at the end of last year, so it’s good to see that support will be added into the mainline Linux kernel with the upcoming release 5.14, as spotted by Phoronix.
Although effectively a Raspberry Pi 4 trapped in a keyboard like a genie in a bottle, there are a few differences between the two SBCs - the CPU of the Raspberry Pi 400 is clocked at 1.8 GHz, 300 MHz more than the Raspberry Pi 4. The speed boost is largely due to better thermals, as we discovered in our review. The Raspberry Pi 400 also features a different Wi-Fi chip, a soft power button (the first Pi to have a power button), and the 400 lacks the Pi 4s activity LED.
The 4B received mainline kernel support back in 2020 with version 5.7. For Kernel 5.14 no driver changes were required for the Raspberry Pi 400, merely a DeviceTree addition was made to support the CPU speed, Wi-Fi and ACT LED. By adding the Raspberry Pi 400 it means that, should the developer decide to take advantage of it, Pi 400 support will be available on any Linux distro based on the mainline kernel. The current version of Raspberry Pi OS is using the Long Term Support version of kernel 5.10, which brought improved support for the Pi 400, making the upgrade in March this year. Before that, it used version 5.4 LTS.
Kernel 5.14 has yet to appear on kernel.org, with the latest stable release at 5.12.10 and a release candidate in the wild for 5.13.